Fluid smulation start Time
Set your framerate to 30fps, (easier to calculate), and set the fluid domain to start at 20 and to end a certain amount of seconds later. Now there is a trick to this: the numbers here are the duration of the animation divided by the framerate of your animation currently. I.e. 300 frames / 30fps = 10 fluid seconds. If you want to end your fluid simulation at frame 900, then set the fluid domain to end at 30 seconds. Here is where you control these settings: